AAPG Bulletin; October 2007; v. 91; no. 10;
p. 1467-1498; DOI: 10.1306/05210705161
© 2007 American Association of Petroleum Geologists (AAPG)
Hierarchies of overpressure retardation of organic matter maturation: Case studies from petroleum basins in China
Fang Hao1,
Huayao Zou2,
Zaisheng Gong3,
Shigang Yang4 and
Zhiping Zeng5
1 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Changping, Beijing 102249, People's Republic of China; present address: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, People's Republic of China; haofang{at}cup.edu.cn
2 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Changping, Beijing 102249, People's Republic of China
3 China National Offshore Oil Corporation, Beijing 100027, People's Republic of China
4 State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, People's Republic of China
5 State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, People's Republic of China
Fang Hao received his Ph.D. from the China University of Geosciences in 1995. He is now a professor of geology at the China University of Petroleum. He has conducted petroleum geology and geochemistry studies in several Chinese basins, including the Bohai Bay, Junggar, Yinggehai, and Qiongdongnan basins. His interest is now in the study of petroleum generation, migration, and accumulation in overpressured sedimentary basins.
Huayao Zou received his Ph.D. from the China University of Geosciences and is now an associate professor at the China University of Petroleum. He spent 2 years as postdoctoral research fellow studying petroleum generation and accumulation in the Bohai Bay Basin before he joined the university. His recent interest is in the study of petroleum accumulation mechanism in lacustrine fault basins.
Zaisheng Gong graduated from Beijing Geological College in 1962 and is the chief scientist of the China National Offshore Oil Cooperation (CNOOC) and a professor at the China University of Geosciences. He held various technical and managerial positions in several onshore oil fields before he joined CNOOC. He has done petroleum geology studies in many Chinese basins and is the author of several books. His recent interest is in the study of petroleum accumulation mechanisms in offshore Chinese basins.
Shigang Yang graduated from Xinan Petroleum Institute in 1982 and is now an on-duty doctoral student of the China University of Geosciences. He held various technical positions in the Zhongyuan Oil Cooperation and has conducted petroleum geology studies in the Bohai Bay Basin for 15 years. His interest is now in the study of petroleum accumulation in the Bohai Bay Basin.
Zhiping Zeng received his M.S. degree from the China University of Geosciences in 2003. He is now a doctoral student at the university. His interest is in the study of the generation and development of overpressures in sedimentary basins.
The effects of overpressure on different aspects of organic matter maturation have been examined in three basins using multiple parameters. Overpressure in the Yinggehai Basin has retarded kerogen maturation, hydrocarbon generation, and thermal cracking of long-chain normal hydrocarbons, as well as evolution of isoprenoid hydrocarbons. Overpressure in the Dongpu depression, Bohai Bay Basin, seems to have retarded the maturation of bulk kerogens reflected by Rock-Eval Tmax, the thermal cracking of long-chain normal hydrocarbons, and the evolution of isoprenoid hydrocarbons, but seems to have had no detectable effects on vitrinite reflectance. Overpressure in the Qiongdongnan Basin has had no detectable retardation effects on all aspects of organic matter maturation. The observed phenomena suggest differential retardation of organic matter maturation (that is, different organic matter maturation reactions and different maturity parameters have been retarded by overpressure to different degrees in the same overpressured system) and four hierarchies of overpressure retardation. Hierarchy I retardation is defined as the state where the overpressure has retarded all aspects of organic matter maturation and is proposed to have been caused by the combination of high formation pressure and excess pressure, a high-water/organic matter ratio, and strong retention of reaction products in an early-developed, strong, persistent overpressured system. Hierarchy II retardation refers to the case in which all aspects of organic matter maturation except the maturation of hydrogen-poor kerogens, especially vitrinite, have been retarded and seem to have been caused by early-developed, moderate to strong, persistent overpressure. Hierarchy III retardation refers to the situation where overpressure has retarded only the thermal cracking of liquid hydrocarbons, but has had no detectable effect on the maturation of both hydrogen-rich and hydrogen-poor kerogens, and is proposed to have been caused by moderate to strong, persistent overpressures that began to develop around peak oil generation. Hierarchy IV retardation is defined as the situation where overpressure has had no detectable retardation on all aspects of organic matter maturation and may have been caused by cases wherein the overpressure developed too late, the intensity of the overpressure was too low, the duration of the overpressure was too short, or overpressured fluids had been expelled frequently. Resulting from both the diversities of organic matter maturation reactions and the complexities of overpressure generation and development, the hierarchies of overpressure retardation in different basins may be quite different, and it is necessary to use multiple parameters to understand the evolution of the petroleum systems in overpressured basins.
Copyright © 2009 by American Association of Petroleum Geologists (AAPG)
